No abstract

In this article, the authors attempt to treat both strong m i s t i n g and slight twisting of fiber via a consistent asymptotic approach to the coupled-mode theory. In strong twisting, an admirably simple and useful asymptotic equation is derived in the form R f = const., which relates the minimum required twist rate 7 with the minimum allowable radius of curvature R In slight twisting an oscillatory pattern of the polarization behauior clearly reveals the advantageous feature of a twist-spun fiber, which is made by a prior spinning of the fiber before a twi3ting. 0 1995 John Wiley & Sons, Inc. Received 11-30-94Microwave and Optical Technology Letters, 9/1,37-41 0 1995 John Wiley & Sons, Inc. KEY TERMS Complex pemrittiuq naeasmments, complex permeability measurements, pariialb filled waveguide ABSTRACTA partially filled waveguide is presented to measure complex permittivity and permeability simultaneously at microwave frequency in this article.The mode-matching method is used to analyze the higher-order modes in the waveguide. Experimental results a p e well with theoretical results. 0 I995 John uliley & Sons, Inc.

-The rapid growth of mobile communications since the introduction of GSM has challenged the industry for designing terminals of reduced size, cost and power consumption. The efficiency and size trade-offs of the antenna on such terminals become an important issue. On the other hand, multi-band operation covering the existing GSM900/DCS1800 and the future UMTS bands is another significant subject of investigation in the mobile phone industry. In this paper, different methods for tuning the planar inverted-F antenna (PIFA) are discussed, in particular with regard to the positioning of the short pins and the introduction of tuning capacitors. A reduced size dual band fine tuned PIFA for the GSM900/DCS1800 bands is introduced and its performance demonstrated. Finally, a technique employing reversed biased varactors for electronically tuning the PIFA is presented.

The problem of double edge diffraction in the near‐field region of a coplanar skewed edge geometry, illuminated by a plane wave, is studied asymptotically via an extended spectral theory of diffraction approach. The resulting uniform dyadic double edge diffraction coefficient is expressed in terms of a universal integral (the generalized Fresnel integral) and remains valid when any one of the edges is within the transition region of a singly diffracted wave, while it asymptotically reduces to the ordinary geometrical theory of diffraction double diffraction coefficient elsewhere. Comparisons with method of moments computations for radiation patterns of sources in the vicinity of flat plate structures demonstrate the validity of the asymptotic approximation.

-The rapid growth of mobile communications since the introduction of GSM has challenged the industry for designing terminals of reduced size, cost and power consumption. The efficiency and size trade-offs of the antenna on such terminals become an important issue. On the other hand, multi-band operation covering the existing GSM900/DCS1800 and the future UMTS bands is another significant subject of investigation in the mobile phone industry. In this paper, different methods for tuning the planar inverted-F antenna (PIFA) are discussed, in particular with regard to the positioning of the short pins and the introduction of tuning capacitors. A reduced size dual band fine tuned PIFA for the GSM900/DCS1800 bands is introduced and its performance demonstrated. Finally, a technique employing reversed biased varactors for electronically tuning the PIFA is presented.